In the event of the whole or a part of a fan blade becoming detached from a fan of a gas turbine engine, it is necessary for the casing around the fan (the fan case) to contain the ejected blade in order to prevent further damage to other engines and the fuselage of the aircraft. Such a blade-off event, and particularly the containment of the blade by the fan case, can create a travelling wave to form around the fan case periphery.
A gas turbine engine typically has a number of pieces of ancillary equipment attached to the fan case. The travelling wave which may occur in a blade-off event, as described above, will interact with and disturb any such components which lie within the amplitude of its path. This may generate abnormally high forces and accelerations which can cause the component and/or mounting point of the component to the fan-case to fail. Where the mounting point of the component to the fan case fails, this may also cause damage to the other engines and the fuselage of the aircraft.
In general terms, the magnitude of the force placed on the mounting point can be characterised by the intimacy of the wave to the component and the mass of the component. For normal conditions, the maximum strength required at a mounting point for safe and continuous engine-running can be gained from test data and/or theoretical modelling.
Where it is not possible to prevent failure at the mounting point, it may be possible to retain the component following failure of the mounting point using a wire lanyard. The wire lanyard may be sufficiently strong to prevent the component from being ejected from the engine. However, such a wire lanyard allows uncontrolled free movement of the component, and, when subjected to the out-of-balance forces which ensue following a blade-off event, this can result in failure of the component. Clearly, this is undesirable where the component provides a critical function in the flight of the aircraft.
Alternatively, a ‘catcher-bracket’ may be used to ‘catch’ such ancillary equipment if a catastrophic event causes failure of the mounting point to the fan case. Such catcher-brackets remain load and stress-free during normal use and are only responsible for retaining the ancillary equipment if the working bracket or structure fails.
However, catcher-brackets require precise and accurate setup to ensure that they are positioned an appropriate distance from the component. If this is not the case, the catcher bracket may be exposed to unwanted intermittent loading where the distance is too small, and may not perform its function where the distance is too large.
Furthermore, whilst wire lanyards and catcher brackets mitigate the effects of the failure of a mounting point, they do not prevent the failure from occurring. Consequently, it is still necessary to replace the mounting bracket or structure.
The present invention seeks to provide a safety connector which overcomes some or all of the problems associated with the prior art devices described above.